Is there no CDN? This feels like it's a non-issue if there's a CDN.
We're going to put Cloudflare in front of our Vercel site and control cache for SSR pages with Cache-Control headers.
Last startup, we ran Astro.js behind CloudFront and we were able to serve pretty large volume of public-facing traffic from just 2 server nodes with 3-tiered caching (Redis for data caching, application level output caching, and CloudFront with CF doing a lot of the heavy lifting)